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That's just not true. You'll need to give a specific example of which apps are like this on Android. I'm writing this using a LineageOS phone with no proprietary or closed source apps on it right now.
This is true and can be verified by anyone by installing random applications from Google Play Store without having Google Play Services installed. Since relatively recently, you can use some of them via microG, but compatibility varies. Sure, there's F-Droid and FLOSS software for Android, but if you're already willing to limit yourself to FLOSS Android apps you may very well limit yourself to FLOSS GNU/Linux apps to…
Secondly, you claim limiting yourself to FLOSS android means you might as well just use FLOSS Linux. But that doesn't make sense because the purely open source elements of the android ecosystem work far better than the pure Linux ecosystem, which is my original point. There is no advantage that you can point to for GNU/Linux over Android/Linux other than just being "pure Linux". Android is fully open source and can be easily run unencumbered by proprietary google software. And there is vastly more open source software that is mobile friendly and compatible for Android/Linux than GNU/Linux.